Research is directed toward genetic mechanisms controlling cellular differentiation in a eukaryote, Drosophila. The approach has been the selection of a specific protein, gamma-amylase, as an indicator of the state of differentiation of tissues; factors that regulate its synthesis, properties, location and ultimate fate are being analyzed. A system is being developed to selectively screen for mutations of "regulatory genes" which may control the structural gene for amylase, Amy. Amy has been located genetically by means of electrophoretic variants of the enzyme in D. melanogaster and D. hydei. The gene is tandemly duplicated in the former species; yet the duplicated loci or their products are independently regulated. It is hoped that the control mechanisms involved here can be defined. In the meantime, efforts are being concentrated on D. hydei, which provides a simpler system for analysis. Here Amy does not appear to be duplicated and diet-induced "puffing" at the locus believed to be Amy in polytene chromosomes of the posterior midgut cells can be analyzed cytologically. This puffing correlates with induction of midgut-specific amylase activity. Mutations altering this cytological sign of transcription will be selected, provided de novo synthesis of amylase can be correlated with the induced puffing activity. By the application of labelling and specific antibody techniques, amylase synthesis will be quantitated, as well as its degradation; mutations affecting these, ie. mutants controlling amylase at the translational level or higher, may thus be distinguished. This system will eventually be adapted to D. Melanogaster. Amylase isozymes from different Amy strains have been purified to molecular homogeneity and are being characterized at the molecular level, e.g. molecular weight, subunit structure, amino acid analysis, peptide mapping, amino acid sequencing, etc. Antibodies have been prepared against amylases from hydei and melanogaster. Labelled antibo dy techniques have localized amylase intracellularly in the midgut during development; mutations altering amylase localization are being sought.